galactic centre

A Dictionary of Astronomy | 1997 | 700+ words | Copyright

galactic centre The very central region or nucleus of our Galaxy, 26 000 l.y. away in the constellation Sagittarius; coordinates RA 17h 46m, dec. −28° 56′. There is a clumpy ring of gas (rich in molecules) and dust about 5–15 l.y. from the exact centre. Inside this is a dense star cluster around the bright radio source Sagittarius A*, which is believed to mark the very centre of the Galaxy. There is strong evidence for a supermassive black hole at the centre of our Galaxy. The orbits of stars in this region imply the existence of a central object of 3–4 million solar masses within a radius less than 0.01 parsec. No object or system other than a black hole could be stable at such a large density. Although highly obscured by dust from optical observation, the galactic centre has been extensively studied at infrared, radio, X-ray, and gamma-ray wavelengths.

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